The present invention relates generally to improvements in attitude control systems (ACS) for spacecraft and more particularly to a novel propellant tank resupply system and method for increasing ACS propellant usage capability through resupply of the ACS tanks during operation of the engines of the primary propulsion system.
An increasing demand is being experienced for the deployment of large, heavy satellites into high energy earth orbits. Anticipated propulsion requirements for placing the spacecraft and other associated payloads of planned missions into geosynchronous orbits far exceed the capabilities of existing orbit transfer stages. The shuttle orbiter may be used for most missions in order to to place satellites into low earth orbit; auxiliary propulsion stages on the satellites may then be used to transfer the satellites into operating earth orbits. Upon achieving its operating orbit, however, a satellite will require additional propulsive energy for station keeping, three-axis attitude control, and threat evasion.
Because future satellite systems will likely be characterized by substantial payload weights, new high-performance, pump-fed rocket engines will be included in many of the associated propulsion systems for orbital maneuvering. The ACS for each orbiting satellite could, however, employ off-the-shelf pressure-fed thrusters to minimize system costs and to improve operational reliability. Due to the difference in operating inlet pressures for the primary propulsion system engines as compared to the ACS thruster inlet pressures in existing systems, large low-pressure propellant storage tanks would be used for the pump-fed main propulsive engines, while small high-pressure propellant tanks or accumulators would be used for the pressure-fed ACS thrusters.
A problem associated with this propulsion system approach is that of providing sufficient ACS propellant capacity to satisfy mission uncertainties. The ACS propellant requirements are difficult to predict in advance, and this problem is compounded by the required long on-orbit stay times (7-10 years) anticipated for future satellites. Enhanced mission flexibility could be achieved in future satellites using the ACS propellant tank resupply method described herein.
The present invention provides a propellant tank resupply system which may be used to resupply the ACS thruster engines on a satellite. During primary engine burnoff, satellite propellants (fuel and oxidizer) are tapped off the respective turbopump inducer exits for recharging the separate ACS fuel and oxidizer propellant tanks. The resupply system of the present invention obviates the need for additional high pressure storage tanks for pressurizing the ACS propellant tanks.
It is, therefore, a principal object of the present invention to provide an improved attitude control system for a spacecraft.
It is a further object of the invention to provide a system and method for recharging the propellant tanks of the attitude control system of a spacecraft.
It is yet another object of the invention to provide a system and method for replenishing under pressure the propellant tanks of the attitude control system of a spacecraft.
These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.